1. Field of the Invention
The present invention relates to a solid-state image capturing device, such as a CCD image sensor and a CMOS image sensor, provided with at least any of openings of electrode wiring layers, color filters and microlenses above a plurality of light receiving elements as an image capturing region, for taking an image light from a subject by the plurality of light receiving elements; a solid-state image capturing apparatus provided with the solid-state image capturing device and an image capturing optical system in front of the solid-state image capturing device; and an electronic information device having, for example, a digital camera (e.g., digital video camera, digital still camera), an image input camera, a scanner, a facsimile and a cell phone device equipped with a camera, using the solid-state image capturing device or the solid-state image capturing apparatus as an image input device in the image capturing section.
2. Description of the Related Art
It has been conventionally known that a microlens array is arranged on a light incident side of a plurality of light receiving elements and an incident light is focused on the light receiving elements, so that the amount of unused light is decreased and the focusing rate is improved.
On the other hand, with respect to a characteristic of an output angle of an image capturing optical system, it is known that a chief ray enters from a normal direction to a light receiving region surface along an optical axis at the center of the light receiving region of a solid-state image capturing device while the chief ray enters the periphery (other than the center) of the light receiving region at an angle (at a tilt). Herein, the chief ray is defined as a light that passes through the center of an aperture stop in an image capturing optical system. If there is no aperture stop provided, the chief ray is defined as a light that passes through the center of a lens.
FIG. 8 is a plane view showing an effective pixel region of a conventional solid-state image capturing device, using a UXGA as an example.
In FIG. 8, the effective pixel region 100 of the conventional solid-state image capturing device is a rectangle. In a case where the solid-state image capturing device is, for example, a UXGA, the UXGA has a large number of light receiving elements with effective pixels of 1200 (row)×1600 (column). When the center (an intersection point on diagonal lines) of the effective pixel region 100 is defined as an image height of “0”, the four corners of the rectangle effective pixel region 100 can be defined as an image height of “100%”. Therefore, the image height indicates how far away the light ray is from the center in a concentric fashion. The image height of “0” of the effective pixel region exists on the optical axis as long as variation arises at the time of manufacturing or a special use is assumed.
FIG. 9 is a longitudinal cross sectional view of an essential structure showing a state where a chief ray is entering with an incident angle into an image capturing region of the solid-state image capturing device in FIG. 8.
In FIG. 9, the chief ray enters the effective pixel region 100 through a lens 101 functioning as an image capturing optical system. At that time, light 102, which enters the lens 101 from the optical axis direction, enters the center of the effective pixel region 100, and light 103, which enters being tilted from the optical axis, enters the periphery of the effective pixel region 100. Herein, the angle with the most intense amount of light entering the image capturing optical system is defined as the incident angle of the chief ray. The incident angle (CRA; chief ray angle) to the effective pixel region 100 increases its gradient as the angle moves from the center of the efficient pixel region 100 to the periphery thereof. The chief ray incident angle also changes depending on the type of the lens 101. In FIG. 9, there is only one lens, but there could be a case where more than one lens is used. The shape of the lens includes not only a spherical shape but also a combination of a spherical shape and an aspherical shape of a few lenses, or only an aspherical shape. Therefore, various characteristics for the chief ray incident angle exist depending on the lens 101. An exemplary chief ray incident angle is schematically shown in FIG. 10. The chief ray enters at the angle shown in FIG. 10 towards the image height of the effective pixel region 100 of the solid-state image capturing device in FIG. 8.
Because the chief ray incident angle tilts more as it moves from the center of the efficient pixel region (light receiving region) 100 to the periphery thereof, Reference 1, for example, discloses a method for arranging microlenses in such a manner that, as going farther from the center portion of the light receiving region 100, the arrangement pitch of the microlenses in the light receiving region 100 gradually becomes smaller than the arrangement pitch of the light receiving elements, and thereby the microlenses come near towards the side of the center portion, so that the focusing rate increases. This is shown in FIG. 11.
FIG. 11 is a graph showing a shift amount in relation to a light receiving element of a microlens as well as a relationship between an arrangement pitch of a microlens and an image height with respect to a conventional solid-state image capturing apparatus disclosed in Reference 1.
As shown in FIG. 11, the shift amount of the microlenses in relation to the light receiving elements is set to be gradually larger as going farther from the center portion (image height “0”) of the light receiving region 100 according to the conventional solid-state image capturing apparatus. On the contrary, the arrangement pitch of the microlenses is set to be gradually smaller as going farther from the center portion (image height “0”) of the light receiving region 100. As a result, an incident light (subject light) which enters off to the side at the periphery of the light receiving region 100 is focused on the light receiving elements, thereby implementing shading correction.
However, various lenses with different characteristics as output characteristics of an image capturing optical system (an aspherical lens shown in FIG. 12 as an example) are used in accordance with the use of the solid-state image capturing apparatus in recent years. Therefore, lenses with a chief ray characteristic, as shown in FIG. 13, in which, as the image height increases from an image height 0 to a certain image height, the incident angle increases, after which it decreases, are used more often; and it is insufficient to merely use a method for arranging microlenses in such a manner that the arrangement pitch of the microlenses gradually becomes smaller than the arrangement pitch of the light receiving elements.
Accordingly, Reference 2, for example, discloses a method for increasing the arrangement pitch of microlenses in a part from the center portion to a predetermined position of the periphery portion and decreasing the arrangement pitch in a part from the predetermined position of the periphery portion to the outer side. This is shown in FIG. 14.
FIG. 14 is a graph showing a shift amount of a microlens in relation to a light receiving element as well as a relationship between an arrangement pitch of a microlens and an image height with respect to a conventional solid-state image capturing apparatus disclosed in Reference 2. In FIG. 14, the vertical axis indicates a shift amount of microlenses in relation to the light receiving elements as well as an arrangement pitch of microlenses, while the transversal axis indicates an image height.
As shown in FIG. 14, the conventional solid-state image capturing apparatus is set in such a manner that the shift amount of the microlenses in relation to the light receiving elements becomes gradually larger as the distance increases from the center (image height “0”) of the light receiving region 100, while the arrangement pitch of the microlenses is set to become gradually smaller between the center portion and the periphery portion with the 80% of the image height in the light receiving region 100. Next, on the contrary with respect to the periphery portion that is further away past the point of image height 80%, the shift amount of the microlenses in relation to the light receiving elements is set to become gradually smaller as the distance increases from the center (image height 0%), while the arrangement pitch of the microlenses is set to become gradually larger. This configuration is said to make a correction for shading possible even in a case where an output angle of a chief ray from an image capturing optical system does not simply increase as an image height from an optical axis increases.
Reference 1: Japanese patent No. 2600250
Reference 2: Japanese Laid-Open Publication No. 2004-228645